In physics, an **electronvolt** (symbol **eV**, also written **electron-volt** and **electron volt**) is the measure of an amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in vacuum. When used as a unit of energy, the numerical value of 1 eV in joules (symbol J) is equivalent to the numerical value of the charge of an electron in coulombs (symbol C). Under the 2019 redefinition of the SI base units, this sets 1 eV equal to the exact value 1.602176634×10^{−19} J.^{ [1] }

- Definition and use
- Relation to other physical properties and units
- Mass
- Momentum
- Distance
- Temperature
- Wavelength
- Scattering experiments
- Energy comparisons
- Per mole
- See also
- References
- External links

Historically, the electronvolt was devised as a standard unit of measure through its usefulness in electrostatic particle accelerator sciences, because a particle with electric charge *q* gains an energy *E* = *qV* after passing through a voltage of *V.* Since *q* must be an integer multiple of the elementary charge *e* for any isolated particle, the gained energy in units of electronvolts conveniently equals that integer times the voltage.

An electronvolt is the amount of kinetic energy gained or lost by a single electron accelerating from rest through an electric potential difference of one volt in vacuum. Hence, it has a value of one volt, 1 J/C, multiplied by the elementary charge *e* = 1.602176634×10^{−19} C.^{ [2] } Therefore, one electronvolt is equal to 1.602176634×10^{−19} J.^{ [1] }

The electronvolt (eV) is a unit of energy, but is not an SI unit. It is a common unit of energy within physics, widely used in solid state, atomic, nuclear, and particle physics, and high-energy astrophysics. It is commonly used with SI prefixes milli-, kilo-, mega-, giga-, tera-, peta- or exa- (meV, keV, MeV, GeV, TeV, PeV and EeV respectively). The SI unit of energy is the joule (J).

In some older documents, and in the name Bevatron, the symbol BeV is used, where the "B" stands for billion. The symbol BeV is therefore equivalent to the GeV.

Measurement | Unit | SI value of unit |
---|---|---|

Energy | eV | 1.602176634×10^{−19} J |

Mass | eV/c^{2} | 1.78266192×10^{−36} kg |

Momentum | eV/c | 5.34428599×10^{−28} kg·m/s |

Temperature | eV/k_{B} | 1.160451812×10^{4} K |

Time | ħ/eV | 6.582119×10^{−16} s |

Distance | ħc/eV | 1.97327×10^{−7} m |

By mass–energy equivalence, the electronvolt corresponds to a unit of mass. It is common in particle physics, where units of mass and energy are often interchanged, to express mass in units of eV/*c*^{2}, where *c* is the speed of light in vacuum (from *E* = *mc*^{2}). It is common to informally express mass in terms of eV as a unit of mass, effectively using a system of natural units with *c* set to 1.^{ [3] } The kilogram equivalent of 1 eV/*c*^{2} is:

For example, an electron and a positron, each with a mass of 0.511 MeV/*c*^{2}, can annihilate to yield 1.022 MeV of energy. A proton has a mass of 0.938 GeV/*c*^{2}. In general, the masses of all hadrons are of the order of 1 GeV/*c*^{2}, which makes the GeV/*c*^{2} a convenient unit of mass for particle physics:^{ [4] }

1 GeV/*c*^{2} = 1.78266192×10^{−27} kg.

The atomic mass constant (*m*_{u}), one twelfth of the mass a carbon-12 atom, is close to the mass of a proton. To convert to electronvolt mass-equivalent, use the formula:

By dividing a particle's kinetic energy in electronvolts by the fundamental constant *c* (the speed of light), one can describe the particle's momentum in units of eV/*c*.^{ [5] } In natural units in which the fundamental velocity constant *c* is numerically 1, the *c* may informally be omitted to express momentum as electronvolts.

in natural units (with )

is a Pythagorean equation. When a relatively high energy is applied to a particle with relatively low rest mass, it can be approximated as in high-energy physics such that an applied energy in units of eV conveniently results in an approximately equivalent change of momentum in units of eV/*c*.

The dimensions of momentum units are T^{−1}LM. The dimensions of energy units are T^{−2}L^{2}M. Dividing the units of energy (such as eV) by a fundamental constant (such as the speed of light) that has units of velocity (T^{−1}L) facilitates the required conversion for using energy units to describe momentum.

For example, if the momentum *p* of an electron is said to be 1 GeV, then the conversion to MKS system of units can be achieved by:

In particle physics, a system of natural units in which the speed of light in vacuum *c* and the reduced Planck constant *ħ* are dimensionless and equal to unity is widely used: *c* = *ħ* = 1. In these units, both distances and times are expressed in inverse energy units (while energy and mass are expressed in the same units, see mass–energy equivalence). In particular, particle scattering lengths are often presented in units of inverse particle masses.

Outside this system of units, the conversion factors between electronvolt, second, and nanometer are the following:

The above relations also allow expressing the mean lifetime *τ* of an unstable particle (in seconds) in terms of its decay width Γ (in eV) via Γ = *ħ*/*τ*. For example, the ^{}B^{0}_{} meson has a lifetime of 1.530(9) picoseconds, mean decay length is *cτ* = 459.7 μm, or a decay width of (4.302±25)×10^{−4} eV.

Conversely, the tiny meson mass differences responsible for meson oscillations are often expressed in the more convenient inverse picoseconds.

Energy in electronvolts is sometimes expressed through the wavelength of light with photons of the same energy:

In certain fields, such as plasma physics, it is convenient to use the electronvolt to express temperature. The electronvolt is divided by the Boltzmann constant to convert to the Kelvin scale:

where *k*_{B} is the Boltzmann constant.

The *k*_{B} is assumed when using the electronvolt to express temperature, for example, a typical magnetic confinement fusion plasma is 15 keV (kiloelectronvolt), which is equal to 174 MK (megakelvin).

As an approximation: *k*_{B}*T* is about 0.025 eV (≈ 290 K/11604 K/eV) at a temperature of 20 °C.

The energy *E*, frequency *v*, and wavelength *λ* of a photon are related by

where *h* is the Planck constant, *c* is the speed of light. This reduces to^{ [6] }

A photon with a wavelength of 532 nm (green light) would have an energy of approximately 2.33 eV. Similarly, 1 eV would correspond to an infrared photon of wavelength 1240 nm or frequency 241.8 THz.

In a low-energy nuclear scattering experiment, it is conventional to refer to the nuclear recoil energy in units of eVr, keVr, etc. This distinguishes the nuclear recoil energy from the "electron equivalent" recoil energy (eVee, keVee, etc.) measured by scintillation light. For example, the yield of a phototube is measured in phe/keVee (photoelectrons per keV electron-equivalent energy). The relationship between eV, eVr, and eVee depends on the medium the scattering takes place in, and must be established empirically for each material.

γ: Gamma rays | MIR: Mid infrared | HF: High freq. |

HX: Hard X-rays | FIR: Far infrared | MF: Medium freq. |

SX: Soft X-rays | Radio waves | LF: Low freq. |

EUV: Extreme ultraviolet | EHF: Extremely high freq. | VLF: Very low freq. |

NUV: Near ultraviolet | SHF: Super high freq. | VF/ULF: Voice freq. |

Visible light | UHF: Ultra high freq. | SLF: Super low freq. |

NIR: Near Infrared | VHF: Very high freq. | ELF: Extremely low freq. |

Freq: Frequency |

Energy | Source |
---|---|

5.25×10^{32} eV | total energy released from a 20 kt nuclear fission device |

12.2 R eV (1.22×10^{28} eV) | the Planck energy |

10 Y eV (1×10^{25} eV) | approximate grand unification energy |

~624 E eV (6.24×10^{20} eV) | energy consumed by a single 100-watt light bulb in one second (100 W = 100 J/s ≈ 6.24×10^{20} eV/s) |

300 E eV (3×10^{20} eV = ~50 J ) | The first ultra-high-energy cosmic ray particle observed, the so-called Oh-My-God particle.^{ [10] } |

2 PeV | two petaelectronvolts, the highest-energy neutrino detected by the IceCube neutrino telescope in Antarctica^{ [11] } |

14 TeV | designed proton center-of-mass collision energy at the Large Hadron Collider (operated at 3.5 TeV since its start on 30 March 2010, reached 13 TeV in May 2015) |

1 TeV | a trillion electronvolts, or 1.602×10^{−7} J, about the kinetic energy of a flying mosquito ^{ [12] } |

172 GeV | rest energy of top quark, the heaviest measured elementary particle |

125.1±0.2 GeV | energy corresponding to the mass of the Higgs boson, as measured by two separate detectors at the LHC to a certainty better than 5 sigma ^{ [13] } |

210 MeV | average energy released in fission of one Pu-239 atom |

200 MeV | approximate average energy released in nuclear fission fission fragments of one U-235 atom. |

105.7 MeV | rest energy of a muon |

17.6 MeV | average energy released in the nuclear fusion of deuterium and tritium to form He-4; this is 0.41 PJ per kilogram of product produced |

2 MeV | approximate average energy released in a nuclear fission neutron released from one U-235 atom. |

1.9 MeV | rest energy of up quark, the lowest mass quark. |

1 MeV (1.602×10^{−13} J) | about twice the rest energy of an electron |

1 to 10 keV | approximate thermal temperature, , in nuclear fusion systems, like the core of the sun, magnetically confined plasma, inertial confinement and nuclear weapons |

13.6 eV | the energy required to ionize atomic hydrogen; molecular bond energies are on the order of 1 eV to 10 eV per bond |

1.6 eV to 3.4 eV | the photon energy of visible light |

1.1 eV | energy required to break a covalent bond in silicon |

720 meV | energy required to break a covalent bond in germanium |

< 120 meV | approximate rest energy of neutrinos (sum of 3 flavors)^{ [14] } |

25 meV | thermal energy, , at room temperature; one air molecule has an average kinetic energy 38 meV |

230 μeV | thermal energy, , of the cosmic microwave background |

One mole of particles given 1 eV of energy each has approximately 96.5 kJ of energy – this corresponds to the Faraday constant (*F*≈96485 C⋅mol^{−1}), where the energy in joules of *n* moles of particles each with energy *E* eV is equal to *E*·*F*·*n*.

The **centimetre–gram–second system of units** is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time. All CGS mechanical units are unambiguously derived from these three base units, but there are several different ways in which the CGS system was extended to cover electromagnetism.

In particle physics, a **lepton** is an elementary particle of half-integer spin that does not undergo strong interactions. Two main classes of leptons exist: charged leptons, and neutral leptons. Charged leptons can combine with other particles to form various composite particles such as atoms and positronium, while neutrinos rarely interact with anything, and are consequently rarely observed. The best known of all leptons is the electron.

**Pair production** is the creation of a subatomic particle and its antiparticle from a neutral boson. Examples include creating an electron and a positron, a muon and an antimuon, or a proton and an antiproton. Pair production often refers specifically to a photon creating an electron–positron pair near a nucleus. As energy must be conserved, for pair production to occur, the incoming energy of the photon must be above a threshold of at least the total rest mass energy of the two particles created. Conservation of energy and momentum are the principal constraints on the process. All other conserved quantum numbers of the produced particles must sum to zero – thus the created particles shall have opposite values of each other. For instance, if one particle has electric charge of +1 the other must have electric charge of −1, or if one particle has strangeness of +1 then another one must have strangeness of −1.

The **hartree**, also known as the **Hartree energy**, is the unit of energy in the atomic units system, named after the British physicist Douglas Hartree. Its CODATA recommended value is *E*_{h} = 4.3597447222071(85)×10^{−18} J = 27.211386245988(53) eV.

In atomic physics, the **Bohr magneton** is a physical constant and the natural unit for expressing the magnetic moment of an electron caused by its orbital or spin angular momentum. In SI units, the Bohr magneton is defined as

A **Fermi gas** is an idealized model, an ensemble of many non-interacting fermions. Fermions are particles that obey Fermi–Dirac statistics, like electrons, protons, and neutrons, and, in general, particles with half-integer spin. These statistics determine the energy distribution of fermions in a Fermi gas in thermal equilibrium, and is characterized by their number density, temperature, and the set of available energy states. The model is named after the Italian physicist Enrico Fermi.

In spectroscopy, the **Rydberg constant**, symbol for heavy atoms or for hydrogen, named after the Swedish physicist Johannes Rydberg, is a physical constant relating to the electromagnetic spectra of an atom. The constant first arose as an empirical fitting parameter in the Rydberg formula for the hydrogen spectral series, but Niels Bohr later showed that its value could be calculated from more fundamental constants according to his model of the atom.

In thermodynamics, the **chemical potential** of a species is the energy that can be absorbed or released due to a change of the particle number of the given species, e.g. in a chemical reaction or phase transition. The chemical potential of a species in a mixture is defined as the rate of change of free energy of a thermodynamic system with respect to the change in the number of atoms or molecules of the species that are added to the system. Thus, it is the partial derivative of the free energy with respect to the amount of the species, all other species' concentrations in the mixture remaining constant. When both temperature and pressure are held constant, and the number of particles is expressed in moles, the chemical potential is the **partial molar Gibbs free energy**. At chemical equilibrium or in phase equilibrium, the total sum of the product of chemical potentials and stoichiometric coefficients is zero, as the free energy is at a minimum. In a system in diffusion equilibrium, the chemical potential of any chemical species is uniformly the same everywhere throughout the system.

In particle physics, the **W and Z bosons** are vector bosons that are together known as the **weak bosons** or more generally as the **intermediate vector bosons**. These elementary particles mediate the weak interaction; the respective symbols are ^{}W^{+}_{}, ^{}W^{−}_{}, and ^{}Z^{0}_{}. The ^{}W^{±}_{} bosons have either a positive or negative electric charge of 1 elementary charge and are each other's antiparticles. The ^{}Z^{0}_{} boson is electrically neutral and is its own antiparticle. The three particles each have a spin of 1. The ^{}W^{±}_{} bosons have a magnetic moment, but the ^{}Z^{0}_{} has none. All three of these particles are very short-lived, with a half-life of about 3×10^{−25} s. Their experimental discovery was pivotal in establishing what is now called the Standard Model of particle physics.

The word "mass" has two meanings in special relativity: *invariant mass* is an invariant quantity which is the same for all observers in all reference frames, while the **relativistic mass** is dependent on the velocity of the observer. According to the concept of mass–energy equivalence, invariant mass is equivalent to *rest energy*, while relativistic mass is equivalent to *relativistic energy*.

In electromagnetism, the **magnetic moment** is the magnetic strength and orientation of a magnet or other object that produces a magnetic field. The magnetic moment is typically expressed as a vector. Examples of objects that have magnetic moments include loops of electric current, permanent magnets, elementary particles, composite particles, various molecules, and many astronomical objects.

The **Lawson criterion** is a figure of merit used in nuclear fusion research. It compares the rate of energy being generated by fusion reactions within the fusion fuel to the rate of energy losses to the environment. When the rate of production is higher than the rate of loss, the system will produce net energy. If enough of that energy is captured by the fuel, the system will become self-sustaining and is said to be ignited.

The **Dirac large numbers hypothesis** (**LNH**) is an observation made by Paul Dirac in 1937 relating ratios of size scales in the Universe to that of force scales. The ratios constitute very large, dimensionless numbers: some 40 orders of magnitude in the present cosmological epoch. According to Dirac's hypothesis, the apparent similarity of these ratios might not be a mere coincidence but instead could imply a cosmology with these unusual features:

The **Compton wavelength** is a quantum mechanical property of a particle, defined as the wavelength of a photon the energy of which is the same as the rest energy of that particle. It was introduced by Arthur Compton in 1923 in his explanation of the scattering of photons by electrons.

**Neutrinoless double beta decay (0νββ)** is a commonly proposed and experimentally pursued theoretical radioactive decay process that would prove a Majorana nature of the neutrino particle. To this day, it has not been found.

**Plasma parameters** define various characteristics of a plasma, an electrically conductive collection of charged and neutral particles of various species that responds *collectively* to electromagnetic forces. Such particle systems can be studied statistically, i.e., their behaviour can be described based on a limited number of global parameters instead of tracking each particle separately.

Energy is defined via work, so the SI **unit of energy** is the same as the unit of work – the joule (J), named in honour of James Prescott Joule and his experiments on the mechanical equivalent of heat. In slightly more fundamental terms, 1 joule is equal to 1 newton metre and, in terms of SI base units

A ** g-factor** is a dimensionless quantity that characterizes the magnetic moment and angular momentum of an atom, a particle or the nucleus. It is essentially a proportionality constant that relates the different observed magnetic moments

In strong-field laser physics, **ponderomotive energy** is the cycle-averaged quiver energy of a free electron in an electromagnetic field.

**Heat transfer physics** describes the kinetics of energy storage, transport, and energy transformation by principal energy carriers: phonons, electrons, fluid particles, and photons. Heat is energy stored in temperature-dependent motion of particles including electrons, atomic nuclei, individual atoms, and molecules. Heat is transferred to and from matter by the principal energy carriers. The state of energy stored within matter, or transported by the carriers, is described by a combination of classical and quantum statistical mechanics. The energy is different made (converted) among various carriers. The heat transfer processes are governed by the rates at which various related physical phenomena occur, such as the rate of particle collisions in classical mechanics. These various states and kinetics determine the heat transfer, i.e., the net rate of energy storage or transport. Governing these process from the atomic level to macroscale are the laws of thermodynamics, including conservation of energy.

- 1 2 "2018 CODATA Value: electron volt".
*The NIST Reference on Constants, Units, and Uncertainty*. NIST. 20 May 2019. Retrieved 2019-05-20. - ↑ "2018 CODATA Value: elementary charge".
*The NIST Reference on Constants, Units, and Uncertainty*. NIST. 20 May 2019. Retrieved 2019-05-20. - ↑ Barrow, J. D. (1983). "Natural Units Before Planck".
*Quarterly Journal of the Royal Astronomical Society*.**24**: 24. Bibcode:1983QJRAS..24...24B. - ↑ Gron Tudor Jones. "Energy and momentum units in particle physics" (PDF).
*Indico.cern.ch*. Retrieved 5 June 2022. - ↑ "Units in particle physics".
*Associate Teacher Institute Toolkit*. Fermilab. 22 March 2002. Archived from the original on 14 May 2011. Retrieved 13 February 2011. - ↑ "CODATA Value: Planck constant in eV s". Archived from the original on 22 January 2015. Retrieved 30 March 2015.
- ↑ What is Light? Archived December 5, 2013, at the Wayback Machine – UC Davis lecture slides
- ↑ Elert, Glenn. "Electromagnetic Spectrum, The Physics Hypertextbook". hypertextbook.com. Archived from the original on 2016-07-29. Retrieved 2016-07-30.
- ↑ "Definition of frequency bands on". Vlf.it. Archived from the original on 2010-04-30. Retrieved 2010-10-16.
- ↑ Open Questions in Physics. Archived 2014-08-08 at the Wayback Machine German Electron-Synchrotron. A Research Centre of the Helmholtz Association. Updated March 2006 by JCB. Original by John Baez.
- ↑ "A growing astrophysical neutrino signal in IceCube now features a 2-PeV neutrino". 21 May 2014. Archived from the original on 2015-03-19.
- ↑ Glossary Archived 2014-09-15 at the Wayback Machine - CMS Collaboration, CERN
- ↑ ATLAS; CMS (26 March 2015). "Combined Measurement of the Higgs Boson Mass in pp Collisions at √s=7 and 8 TeV with the ATLAS and CMS Experiments".
*Physical Review Letters*.**114**(19): 191803. arXiv: 1503.07589 . Bibcode:2015PhRvL.114s1803A. doi: 10.1103/PhysRevLett.114.191803 . PMID 26024162. - ↑ Mertens, Susanne (2016). "Direct neutrino mass experiments".
*Journal of Physics: Conference Series*.**718**(2): 022013. arXiv: 1605.01579 . Bibcode:2016JPhCS.718b2013M. doi:10.1088/1742-6596/718/2/022013. S2CID 56355240.

This page is based on this Wikipedia article

Text is available under the CC BY-SA 4.0 license; additional terms may apply.

Images, videos and audio are available under their respective licenses.

Text is available under the CC BY-SA 4.0 license; additional terms may apply.

Images, videos and audio are available under their respective licenses.